74 research outputs found
Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley
TOI-732 is an M dwarf hosting two transiting planets that are located on the
two opposite sides of the radius valley. By doubling the number of available
space-based observations and increasing the number of radial velocity (RV)
measurements, we aim at refining the parameters of TOI-732 b and c. We also use
the results to study the slope of the radius valley and the density valley for
a well-characterised sample of M-dwarf exoplanets. We performed a global MCMC
analysis by jointly modelling ground-based light curves and CHEOPS and TESS
observations, along with RV time series both taken from the literature and
obtained with the MAROON-X spectrograph. The slopes of the M-dwarf valleys were
quantified via a Support Vector Machine (SVM) procedure. TOI-732 b is an
ultrashort-period planet ( d) with a radius
and a mass
(mean density g cm), while the
outer planet at d has ,
, and thus
g cm. Also taking into account our interior structure calculations,
TOI-732 b is a super-Earth and TOI-732 c is a mini-Neptune. Following the SVM
approach, we quantified
,
which is flatter than for Sun-like stars. In line with former analyses, we note
that the radius valley for M-dwarf planets is more densely populated, and we
further quantify the slope of the density valley as
.
Compared to FGK stars, the weaker dependence of the position of the radius
valley on the orbital period might indicate that the formation shapes the
radius valley around M dwarfs more strongly than the evolution mechanisms.Comment: 28 pages (17 in the main text), 18 figures (9 in the main text), 11
tables (7 in the main text). Accepted for publication in A&
Refining the properties of the TOI-178 system with CHEOPS and TESS
The TOI-178 system consists of a nearby late K-dwarf transited by six planets
in the super-Earth to mini-Neptune regime, with orbital periods between 1.9 and
20.7 days. All planets but the innermost one form a chain of Laplace
resonances. Mass estimates derived from a preliminary radial velocity (RV)
dataset suggest that the planetary densities do not decrease in a monotonic way
with the orbital distance to the star, contrary to what one would expect based
on simple formation and evolution models. To improve the characterisation of
this key system and prepare for future studies (in particular with JWST), we
perform a detailed photometric study based on 40 new CHEOPS visits, one new
TESS sector, as well as previously published CHEOPS, TESS, and NGTS data. First
we perform a global analysis of the 100 transits contained in our data to
refine the transit parameters of the six planets and study their transit timing
variations (TTVs). We then use our extensive dataset to place constraints on
the radii and orbital periods of potential additional transiting planets in the
system. Our analysis significantly refines the transit parameters of the six
planets, most notably their radii, for which we now obtain relative precisions
3%, with the exception of the smallest planet for which the
precision is 5.1%. Combined with the RV mass estimates, the measured TTVs allow
us to constrain the eccentricities of planets to , which are found to be
all below 0.02, as expected from stability requirements. Taken alone, the TTVs
also suggest a higher mass for planet than the one estimated from the RVs,
which had been found to yield a surprisingly low density for this planet.
However, the masses derived from the current TTV dataset are very
prior-dependent and further observations, over a longer temporal baseline, are
needed to deepen our understanding of this iconic planetary system.Comment: 20 pages, 5 figures, 9 tables. Accepted for publication in A&
Exploiting timing capabilities of the CHEOPS mission with warm-Jupiter planets
Funding: ACC and TGW acknowledge support from STFC consolidated grant No. ST/M001296/1. This project has received funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme (project FOUR ACES; grant agreement No. 724427)We present 17 transit light curves of seven known warm-Jupiters observed with the CHaracterising ExOPlanet Satellite (CHEOPS). The light curves have been collected as part of the CHEOPS Guaranteed Time Observation (GTO) program that searches for transit-timing variation (TTV) of warm-Jupiters induced by a possible external perturber to shed light on the evolution path of such planetary systems. We describe the CHEOPS observation process, from the planning to the data analysis. In this work, we focused on the timing performance of CHEOPS, the impact of the sampling of the transit phases, and the improvement we can obtain by combining multiple transits together. We reached the highest precision on the transit time of about 13â16 s for the brightest target (WASP-38, G = 9.2) in our sample. From the combined analysis of multiple transits of fainter targets with G â„ 11, we obtained a timing precision of âŒ2 min. Additional observations with CHEOPS, covering a longer temporal baseline, will further improve the precision on the transit times and will allow us to detect possible TTV signals induced by an external perturber.Publisher PDFPeer reviewe
TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS
A large sample of long-period giant planets has been discovered thanks to
long-term radial velocity surveys, but only a few dozen of these planets have a
precise radius measurement. Transiting gas giants are crucial targets for the
study of atmospheric composition across a wide range of equilibrium
temperatures and for shedding light on the formation and evolution of planetary
systems. Indeed, compared to hot Jupiters, the atmospheric properties and
orbital parameters of cooler gas giants are unaltered by intense stellar
irradiation and tidal effects. We identify long-period planets in the
Transiting Exoplanet Survey Satellite (TESS) data as duo-transit events. To
solve the orbital periods of TESS duo-transit candidates, we use the
CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability
period aliases in order to discard or confirm a transit event at a given
period. We also collect spectroscopic observations with CORALIE and HARPS in
order to confirm the planetary nature and measure the mass of the candidates.
We report the discovery of a warm transiting Neptune-mass planet orbiting
TOI-5678. After four non-detections corresponding to possible periods, CHEOPS
detected a transit event matching a unique period alias. Joint modeling reveals
that TOI-5678 hosts a 47.73 day period planet. TOI-5678 b has a mass of 20
(+-4) Me and a radius of 4.91 (+-0.08 Re) . Using interior structure modeling,
we find that TOI-5678 b is composed of a low-mass core surrounded by a large
H/He layer with a mass of 3.2 (+1.7, -1.3) Me. TOI-5678 b is part of a growing
sample of well-characterized transiting gas giants receiving moderate amounts
of stellar insolation (11 Se). Precise density measurement gives us insight
into their interior composition, and the objects orbiting bright stars are
suitable targets to study the atmospheric composition of cooler gas giants.Comment: 17 pages, 10 figures, accepted to A&
Refined parameters of the HD 22946 planetary system and the true orbital period of planet d
Multi-planet systems are important sources of information regarding the
evolution of planets. However, the long-period planets in these systems often
escape detection. HD 22946 is a bright star around which 3 transiting planets
were identified via TESS photometry, but the true orbital period of the
outermost planet d was unknown until now. We aim to use CHEOPS to uncover the
true orbital period of HD 22946d and to refine the orbital and planetary
properties of the system, especially the radii of the planets. We used the
available TESS photometry of HD 22946 and observed several transits of the
planets b, c, and d using CHEOPS. We identified 2 transits of planet d in the
TESS photometry, calculated the most probable period aliases based on these
data, and then scheduled CHEOPS observations. The photometric data were
supplemented with ESPRESSO radial velocity data. Finally, a combined model was
fitted to the entire dataset. We successfully determined the true orbital
period of the planet d to be 47.42489 0.00011 d, and derived precise
radii of the planets in the system, namely 1.362 0.040 R, 2.328
0.039 R, and 2.607 0.060 R for planets b, c, and
d, respectively. Due to the low number of radial velocities, we were only able
to determine 3 upper limits for these respective planet masses, which
are 13.71 M, 9.72 M, and 26.57 M. We estimated that
another 48 ESPRESSO radial velocities are needed to measure the predicted
masses of all planets in HD 22946. Planet c appears to be a promising target
for future atmospheric characterisation. We can also conclude that planet d, as
a warm sub-Neptune, is very interesting because there are only a few similar
confirmed exoplanets to date. Such objects are worth investigating in the near
future, for example in terms of their composition and internal structure
CHEOPS observations of KELT-20 b/MASCARA-2 b: An aligned orbit and signs of variability from a reflective dayside
Occultations are windows of opportunity to indirectly peek into the dayside
atmosphere of exoplanets. High-precision transit events provide information on
the spin-orbit alignment of exoplanets around fast-rotating hosts. We aim to
precisely measure the planetary radius and geometric albedo of the ultra-hot
Jupiter (UHJ) KELT-20 b as well as the system's spin-orbit alignment. We
obtained optical high-precision transits and occultations of KELT-20 b using
CHEOPS observations in conjunction with the simultaneous TESS observations. We
interpreted the occultation measurements together with archival infrared
observations to measure the planetary geometric albedo and dayside
temperatures. We further used the host star's gravity-darkened nature to
measure the system's obliquity. We present a time-averaged precise occultation
depth of 82(6) ppm measured with seven CHEOPS visits and 131(+8/-7) ppm from
the analysis of all available TESS photometry. Using these measurements, we
precisely constrain the geometric albedo of KELT-20 b to 0.26(0.04) and the
brightness temperature of the dayside hemisphere to 2566(+77/-80) K. Assuming
Lambertian scattering law, we constrain the Bond albedo to 0.36(+0.04/-0.05)
along with a minimal heat transfer to the night side. Furthermore, using five
transit observations we provide stricter constraints of 3.9(1.1) degrees on the
sky-projected obliquity of the system. The aligned orbit of KELT-20 b is in
contrast to previous CHEOPS studies that have found strongly inclined orbits
for planets orbiting other A-type stars. The comparably high planetary
geometric albedo of KELT-20 b corroborates a known trend of strongly irradiated
planets being more reflective. Finally, we tentatively detect signs of temporal
variability in the occultation depths, which might indicate variable cloud
cover advecting onto the planetary day side.Comment: 27 pages, 15 figures, Accepted for publication in Astronomy &
Astrophysic
Examining the orbital decay targets KELT-9 b, KELT-16 b, and WASP-4 b, and the transit-timing variations of HD 97658 b,
Context. Tidal orbital decay is suspected to occur for hot Jupiters in particular, with the only observationally confirmed case of this being WASP-12 b. By examining this effect, information on the properties of the host star can be obtained using the so-called stellar modified tidal quality factor QâČâ, which describes the efficiency with which the kinetic energy of the planet is dissipated within the star. This can provide information about the interior of the star. Aims. In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16, and WASP-4 systems in order to find evidence for or against the presence of tidal orbital decay. With this, we want to constrain the QâČâ value for each star. In addition, we aim to test the existence of the transit timing variations (TTVs) in the HD 97658 system, which previously favoured a quadratic trend with increasing orbital period. Methods. Making use of newly acquired photometric observations from CHEOPS (CHaracterising ExOplanet Satellite) and TESS (Transiting Exoplanet Survey Satellite), combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models to the data, namely a constant-period model, an orbital-decay model, and an apsidal-precession model. Results. We find that the KELT-9 system is best described by an apsidal-precession model for now, with an orbital decay trend at over 2 Ï being a possible solution as well. A Keplerian orbit model with a constant orbital period provides the best fit to the transit timings of KELT-16 b because of the scatter and scale of their error bars. The WASP-4 system is best represented by an orbital decay model at a 5 Ï significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find no conclusive evidence for a previously suspected strong quadratic trend in the data
The tidal deformation and atmosphere of WASP-12b from its phase curve
Ultra-hot Jupiters present a unique opportunity to understand the physics and
chemistry of planets at extreme conditions. WASP-12b stands out as an archetype
of this class of exoplanets. We performed comprehensive analyses of the
transits, occultations, and phase curves of WASP-12b by combining new CHEOPS
observations with previous TESS and Spitzer data to measure the planet's tidal
deformation, atmospheric properties, and orbital decay rate. The planet was
modeled as a triaxial ellipsoid parameterized by the second-order fluid Love
number, , which quantifies its radial deformation and provides insight
into the interior structure. We measured the tidal deformation of WASP-12b and
estimated a Love number of (at 3.2) from its
phase curve. We measured occultation depths of ppm and ppm
in the CHEOPS and TESS bands, respectively, while the dayside emission spectrum
indicates that CHEOPS and TESS probe similar pressure levels in the atmosphere
at a temperature of 2900K. We also estimated low geometric albedos of
and in the CHEOPS and TESS passbands,
respectively, suggesting the absence of reflective clouds in the dayside of the
WASP-12b. The CHEOPS occultations do not show strong evidence for variability
in the dayside atmosphere of the planet. Finally, we refine the orbital decay
rate by 12% to a value of -30.230.82 ms/yr.
WASP-12b becomes the second exoplanet, after WASP-103b, for which the Love
number has been measured (at 3) from the effect of tidal deformation in
the light curve. However, constraining the core mass fraction of the planet
requires measuring with a higher precision. This can be achieved with
high signal-to-noise observations with JWST since the phase curve amplitude,
and consequently the induced tidal deformation effect, is higher in the
infrared.Comment: accepted for publication in A&
A pair of Sub-Neptunes transiting the bright K-dwarf TOI-1064 characterised with CHEOPS
Funding: TGW, ACC, and KH acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant ST/R003203/1.We report the discovery and characterization of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in the Transiting Exoplanet Survey Satellite (TESS) photometry. To characterize the system, we performed and retrieved the CHaracterising ExOPlanets Satellite (CHEOPS), TESS, and ground-based photometry, the High Accuracy Radial velocity Planet Searcher (HARPS) high-resolution spectroscopy, and Gemini speckle imaging. We characterize the host star and determine Teff,â=4734±67Kâ , Râ=0.726±0.007Rââ , and Mâ=0.748±0.032Mââ . We present a novel detrending method based on point spread function shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of Pb = 6.44387 ± 0.00003 d, a radius of Rb = 2.59 ± 0.04 Râ, and a mass of Mb=13.5+1.7â1.8 Mâ, whilst TOI-1064 c has an orbital period of Pc=12.22657+0.00005â0.00004 d, a radius of Rc = 2.65 ± 0.04 Râ, and a 3Ï upper mass limit of 8.5 Mâ. From the high-precision photometry we obtain radius uncertainties of âŒ1.6 per cent, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterized sub-Neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further radial velocities are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of massâradius space, and it allow us to identify a trend in bulk densityâstellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets.Publisher PDFPeer reviewe
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